feat: add Anthropic sticky session digest chain matching via Trie

The previous fallback (step 3) in GenerateSessionHash hashed system +
all messages together, producing a different hash each round as the
conversation grew ([a] -> [a,b] -> [a,b,c]). This made fallback sticky
sessions ineffective for multi-turn conversations.

Implement per-message Trie digest chain matching (reusing Gemini's Trie
infrastructure) so that the previous round's chain is always a prefix
of the current round's chain, enabling reliable session affinity.

backend/internal/handler/gateway_handler.go

@@ -22,6 +22,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
 )
 
 // GatewayHandler handles API gateway requests
@@ -212,6 +213,53 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 	if sessionKey != "" {
 		sessionBoundAccountID, _ = h.gatewayService.GetCachedSessionAccountID(c.Request.Context(), apiKey.GroupID, sessionKey)
 	}
+
+	// === Anthropic 内容摘要会话 Fallback 逻辑 ===
+	// 当原有会话标识无效时（sessionBoundAccountID == 0），尝试基于内容摘要链匹配
+	var anthropicDigestChain string
+	var anthropicPrefixHash string
+	var anthropicSessionUUID string
+	useAnthropicDigestFallback := sessionBoundAccountID == 0 && platform != service.PlatformGemini
+
+	if useAnthropicDigestFallback {
+		anthropicDigestChain = service.BuildAnthropicDigestChain(parsedReq)
+		if anthropicDigestChain != "" {
+			userAgent := c.GetHeader("User-Agent")
+			clientIP := ip.GetClientIP(c)
+			anthropicPrefixHash = service.GenerateGeminiPrefixHash(
+				subject.UserID,
+				apiKey.ID,
+				clientIP,
+				userAgent,
+				platform,
+				reqModel,
+			)
+
+			foundUUID, foundAccountID, found := h.gatewayService.FindAnthropicSession(
+				c.Request.Context(),
+				derefGroupID(apiKey.GroupID),
+				anthropicPrefixHash,
+				anthropicDigestChain,
+			)
+			if found {
+				sessionBoundAccountID = foundAccountID
+				anthropicSessionUUID = foundUUID
+				log.Printf("[Anthropic] Digest fallback matched: uuid=%s, accountID=%d, chain=%s",
+					foundUUID[:8], foundAccountID, truncateDigestChain(anthropicDigestChain))
+
+				if sessionKey == "" {
+					sessionKey = service.GenerateAnthropicDigestSessionKey(anthropicPrefixHash, foundUUID)
+				}
+				_ = h.gatewayService.BindStickySession(c.Request.Context(), apiKey.GroupID, sessionKey, foundAccountID)
+			} else {
+				anthropicSessionUUID = uuid.New().String()
+				if sessionKey == "" {
+					sessionKey = service.GenerateAnthropicDigestSessionKey(anthropicPrefixHash, anthropicSessionUUID)
+				}
+			}
+		}
+	}
+
 	// 判断是否真的绑定了粘性会话：有 sessionKey 且已经绑定到某个账号
 	hasBoundSession := sessionKey != "" && sessionBoundAccountID > 0
 
@@ -540,6 +588,20 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 			userAgent := c.GetHeader("User-Agent")
 			clientIP := ip.GetClientIP(c)
 
+			// 保存 Anthropic 内容摘要会话（用于 Fallback 匹配）
+			if useAnthropicDigestFallback && anthropicDigestChain != "" && anthropicPrefixHash != "" {
+				if err := h.gatewayService.SaveAnthropicSession(
+					c.Request.Context(),
+					derefGroupID(apiKey.GroupID),
+					anthropicPrefixHash,
+					anthropicDigestChain,
+					anthropicSessionUUID,
+					account.ID,
+				); err != nil {
+					log.Printf("[Anthropic] Failed to save digest session: %v", err)
+				}
+			}
+
 			// 异步记录使用量（subscription已在函数开头获取）
 			go func(result *service.ForwardResult, usedAccount *service.Account, ua, clientIP string, fcb bool) {
 				ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)

backend/internal/repository/gateway_cache.go

@@ -238,3 +238,41 @@ func (c *gatewayCache) SaveGeminiSession(ctx context.Context, groupID int64, pre
 
 	return c.rdb.Eval(ctx, geminiTrieSaveScript, []string{trieKey}, digestChain, value, ttlSeconds).Err()
 }
+
+// ============ Anthropic 会话 Fallback 方法 (复用 Trie 实现) ============
+
+// FindAnthropicSession 查找 Anthropic 会话（复用 Gemini Trie Lua 脚本）
+func (c *gatewayCache) FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
+	if digestChain == "" {
+		return "", 0, false
+	}
+
+	trieKey := service.BuildAnthropicTrieKey(groupID, prefixHash)
+	ttlSeconds := int(service.AnthropicSessionTTL().Seconds())
+
+	result, err := c.rdb.Eval(ctx, geminiTrieFindScript, []string{trieKey}, digestChain, ttlSeconds).Result()
+	if err != nil || result == nil {
+		return "", 0, false
+	}
+
+	value, ok := result.(string)
+	if !ok || value == "" {
+		return "", 0, false
+	}
+
+	uuid, accountID, ok = service.ParseGeminiSessionValue(value)
+	return uuid, accountID, ok
+}
+
+// SaveAnthropicSession 保存 Anthropic 会话（复用 Gemini Trie Lua 脚本）
+func (c *gatewayCache) SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error {
+	if digestChain == "" {
+		return nil
+	}
+
+	trieKey := service.BuildAnthropicTrieKey(groupID, prefixHash)
+	value := service.FormatGeminiSessionValue(uuid, accountID)
+	ttlSeconds := int(service.AnthropicSessionTTL().Seconds())
+
+	return c.rdb.Eval(ctx, geminiTrieSaveScript, []string{trieKey}, digestChain, value, ttlSeconds).Err()
+}

backend/internal/service/anthropic_session.go

+package service
+
+import (
+	"encoding/json"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Anthropic 会话 Fallback 相关常量
+const (
+	// anthropicSessionTTLSeconds Anthropic 会话缓存 TTL（5 分钟）
+	anthropicSessionTTLSeconds = 300
+
+	// anthropicTrieKeyPrefix Anthropic Trie 会话 key 前缀
+	anthropicTrieKeyPrefix = "anthropic:trie:"
+
+	// anthropicDigestSessionKeyPrefix Anthropic 摘要 fallback 会话 key 前缀
+	anthropicDigestSessionKeyPrefix = "anthropic:digest:"
+)
+
+// AnthropicSessionTTL 返回 Anthropic 会话缓存 TTL
+func AnthropicSessionTTL() time.Duration {
+	return anthropicSessionTTLSeconds * time.Second
+}
+
+// BuildAnthropicDigestChain 根据 Anthropic 请求生成摘要链
+// 格式: s:<hash>-u:<hash>-a:<hash>-u:<hash>-...
+// s = system, u = user, a = assistant
+func BuildAnthropicDigestChain(parsed *ParsedRequest) string {
+	if parsed == nil {
+		return ""
+	}
+
+	var parts []string
+
+	// 1. system prompt
+	if parsed.System != nil {
+		systemData, _ := json.Marshal(parsed.System)
+		if len(systemData) > 0 && string(systemData) != "null" {
+			parts = append(parts, "s:"+shortHash(systemData))
+		}
+	}
+
+	// 2. messages
+	for _, msg := range parsed.Messages {
+		msgMap, ok := msg.(map[string]any)
+		if !ok {
+			continue
+		}
+		role, _ := msgMap["role"].(string)
+		prefix := rolePrefix(role)
+		content := msgMap["content"]
+		contentData, _ := json.Marshal(content)
+		parts = append(parts, prefix+":"+shortHash(contentData))
+	}
+
+	return strings.Join(parts, "-")
+}
+
+// rolePrefix 将 Anthropic 的 role 映射为单字符前缀
+func rolePrefix(role string) string {
+	switch role {
+	case "assistant":
+		return "a"
+	default:
+		return "u"
+	}
+}
+
+// BuildAnthropicTrieKey 构建 Anthropic Trie Redis key
+// 格式: anthropic:trie:{groupID}:{prefixHash}
+func BuildAnthropicTrieKey(groupID int64, prefixHash string) string {
+	return anthropicTrieKeyPrefix + strconv.FormatInt(groupID, 10) + ":" + prefixHash
+}
+
+// GenerateAnthropicDigestSessionKey 生成 Anthropic 摘要 fallback 的 sessionKey
+// 组合 prefixHash 前 8 位 + uuid 前 8 位，确保不同会话产生不同的 sessionKey
+func GenerateAnthropicDigestSessionKey(prefixHash, uuid string) string {
+	prefix := prefixHash
+	if len(prefixHash) >= 8 {
+		prefix = prefixHash[:8]
+	}
+	uuidPart := uuid
+	if len(uuid) >= 8 {
+		uuidPart = uuid[:8]
+	}
+	return anthropicDigestSessionKeyPrefix + prefix + ":" + uuidPart
+}

backend/internal/service/anthropic_session_test.go

+package service
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestBuildAnthropicDigestChain_NilRequest(t *testing.T) {
+	result := BuildAnthropicDigestChain(nil)
+	if result != "" {
+		t.Errorf("expected empty string for nil request, got: %s", result)
+	}
+}
+
+func TestBuildAnthropicDigestChain_EmptyMessages(t *testing.T) {
+	parsed := &ParsedRequest{
+		Messages: []any{},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	if result != "" {
+		t.Errorf("expected empty string for empty messages, got: %s", result)
+	}
+}
+
+func TestBuildAnthropicDigestChain_SingleUserMessage(t *testing.T) {
+	parsed := &ParsedRequest{
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	parts := splitChain(result)
+	if len(parts) != 1 {
+		t.Fatalf("expected 1 part, got %d: %s", len(parts), result)
+	}
+	if !strings.HasPrefix(parts[0], "u:") {
+		t.Errorf("expected prefix 'u:', got: %s", parts[0])
+	}
+}
+
+func TestBuildAnthropicDigestChain_UserAndAssistant(t *testing.T) {
+	parsed := &ParsedRequest{
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "hi there"},
+		},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	parts := splitChain(result)
+	if len(parts) != 2 {
+		t.Fatalf("expected 2 parts, got %d: %s", len(parts), result)
+	}
+	if !strings.HasPrefix(parts[0], "u:") {
+		t.Errorf("part[0] expected prefix 'u:', got: %s", parts[0])
+	}
+	if !strings.HasPrefix(parts[1], "a:") {
+		t.Errorf("part[1] expected prefix 'a:', got: %s", parts[1])
+	}
+}
+
+func TestBuildAnthropicDigestChain_WithSystemString(t *testing.T) {
+	parsed := &ParsedRequest{
+		System: "You are a helpful assistant",
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	parts := splitChain(result)
+	if len(parts) != 2 {
+		t.Fatalf("expected 2 parts (s + u), got %d: %s", len(parts), result)
+	}
+	if !strings.HasPrefix(parts[0], "s:") {
+		t.Errorf("part[0] expected prefix 's:', got: %s", parts[0])
+	}
+	if !strings.HasPrefix(parts[1], "u:") {
+		t.Errorf("part[1] expected prefix 'u:', got: %s", parts[1])
+	}
+}
+
+func TestBuildAnthropicDigestChain_WithSystemContentBlocks(t *testing.T) {
+	parsed := &ParsedRequest{
+		System: []any{
+			map[string]any{"type": "text", "text": "You are a helpful assistant"},
+		},
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	parts := splitChain(result)
+	if len(parts) != 2 {
+		t.Fatalf("expected 2 parts (s + u), got %d: %s", len(parts), result)
+	}
+	if !strings.HasPrefix(parts[0], "s:") {
+		t.Errorf("part[0] expected prefix 's:', got: %s", parts[0])
+	}
+}
+
+func TestBuildAnthropicDigestChain_ConversationPrefixRelationship(t *testing.T) {
+	// 核心测试：验证对话增长时链的前缀关系
+	// 上一轮的完整链一定是下一轮链的前缀
+	system := "You are a helpful assistant"
+
+	// 第 1 轮: system + user
+	round1 := &ParsedRequest{
+		System: system,
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+	chain1 := BuildAnthropicDigestChain(round1)
+
+	// 第 2 轮: system + user + assistant + user
+	round2 := &ParsedRequest{
+		System: system,
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "hi there"},
+			map[string]any{"role": "user", "content": "how are you?"},
+		},
+	}
+	chain2 := BuildAnthropicDigestChain(round2)
+
+	// 第 3 轮: system + user + assistant + user + assistant + user
+	round3 := &ParsedRequest{
+		System: system,
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "hi there"},
+			map[string]any{"role": "user", "content": "how are you?"},
+			map[string]any{"role": "assistant", "content": "I'm doing well"},
+			map[string]any{"role": "user", "content": "great"},
+		},
+	}
+	chain3 := BuildAnthropicDigestChain(round3)
+
+	t.Logf("Chain1: %s", chain1)
+	t.Logf("Chain2: %s", chain2)
+	t.Logf("Chain3: %s", chain3)
+
+	// chain1 是 chain2 的前缀
+	if !strings.HasPrefix(chain2, chain1) {
+		t.Errorf("chain1 should be prefix of chain2:\n  chain1: %s\n  chain2: %s", chain1, chain2)
+	}
+
+	// chain2 是 chain3 的前缀
+	if !strings.HasPrefix(chain3, chain2) {
+		t.Errorf("chain2 should be prefix of chain3:\n  chain2: %s\n  chain3: %s", chain2, chain3)
+	}
+
+	// chain1 也是 chain3 的前缀（传递性）
+	if !strings.HasPrefix(chain3, chain1) {
+		t.Errorf("chain1 should be prefix of chain3:\n  chain1: %s\n  chain3: %s", chain1, chain3)
+	}
+}
+
+func TestBuildAnthropicDigestChain_DifferentSystemProducesDifferentChain(t *testing.T) {
+	parsed1 := &ParsedRequest{
+		System: "System A",
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+	parsed2 := &ParsedRequest{
+		System: "System B",
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+		},
+	}
+
+	chain1 := BuildAnthropicDigestChain(parsed1)
+	chain2 := BuildAnthropicDigestChain(parsed2)
+
+	if chain1 == chain2 {
+		t.Error("Different system prompts should produce different chains")
+	}
+
+	// 但 user 部分的 hash 应该相同
+	parts1 := splitChain(chain1)
+	parts2 := splitChain(chain2)
+	if parts1[1] != parts2[1] {
+		t.Error("Same user message should produce same hash regardless of system")
+	}
+}
+
+func TestBuildAnthropicDigestChain_DifferentContentProducesDifferentChain(t *testing.T) {
+	parsed1 := &ParsedRequest{
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "ORIGINAL reply"},
+			map[string]any{"role": "user", "content": "next"},
+		},
+	}
+	parsed2 := &ParsedRequest{
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "TAMPERED reply"},
+			map[string]any{"role": "user", "content": "next"},
+		},
+	}
+
+	chain1 := BuildAnthropicDigestChain(parsed1)
+	chain2 := BuildAnthropicDigestChain(parsed2)
+
+	if chain1 == chain2 {
+		t.Error("Different content should produce different chains")
+	}
+
+	parts1 := splitChain(chain1)
+	parts2 := splitChain(chain2)
+	// 第一个 user message hash 应该相同
+	if parts1[0] != parts2[0] {
+		t.Error("First user message hash should be the same")
+	}
+	// assistant reply hash 应该不同
+	if parts1[1] == parts2[1] {
+		t.Error("Assistant reply hash should differ")
+	}
+}
+
+func TestBuildAnthropicDigestChain_Deterministic(t *testing.T) {
+	parsed := &ParsedRequest{
+		System: "test system",
+		Messages: []any{
+			map[string]any{"role": "user", "content": "hello"},
+			map[string]any{"role": "assistant", "content": "hi"},
+		},
+	}
+
+	chain1 := BuildAnthropicDigestChain(parsed)
+	chain2 := BuildAnthropicDigestChain(parsed)
+
+	if chain1 != chain2 {
+		t.Errorf("BuildAnthropicDigestChain not deterministic: %s vs %s", chain1, chain2)
+	}
+}
+
+func TestBuildAnthropicTrieKey(t *testing.T) {
+	tests := []struct {
+		name       string
+		groupID    int64
+		prefixHash string
+		want       string
+	}{
+		{
+			name:       "normal",
+			groupID:    123,
+			prefixHash: "abcdef12",
+			want:       "anthropic:trie:123:abcdef12",
+		},
+		{
+			name:       "zero group",
+			groupID:    0,
+			prefixHash: "xyz",
+			want:       "anthropic:trie:0:xyz",
+		},
+		{
+			name:       "empty prefix",
+			groupID:    1,
+			prefixHash: "",
+			want:       "anthropic:trie:1:",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := BuildAnthropicTrieKey(tt.groupID, tt.prefixHash)
+			if got != tt.want {
+				t.Errorf("BuildAnthropicTrieKey(%d, %q) = %q, want %q", tt.groupID, tt.prefixHash, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGenerateAnthropicDigestSessionKey(t *testing.T) {
+	tests := []struct {
+		name       string
+		prefixHash string
+		uuid       string
+		want       string
+	}{
+		{
+			name:       "normal 16 char hash with uuid",
+			prefixHash: "abcdefgh12345678",
+			uuid:       "550e8400-e29b-41d4-a716-446655440000",
+			want:       "anthropic:digest:abcdefgh:550e8400",
+		},
+		{
+			name:       "exactly 8 chars",
+			prefixHash: "12345678",
+			uuid:       "abcdefgh",
+			want:       "anthropic:digest:12345678:abcdefgh",
+		},
+		{
+			name:       "short values",
+			prefixHash: "abc",
+			uuid:       "xyz",
+			want:       "anthropic:digest:abc:xyz",
+		},
+		{
+			name:       "empty values",
+			prefixHash: "",
+			uuid:       "",
+			want:       "anthropic:digest::",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := GenerateAnthropicDigestSessionKey(tt.prefixHash, tt.uuid)
+			if got != tt.want {
+				t.Errorf("GenerateAnthropicDigestSessionKey(%q, %q) = %q, want %q", tt.prefixHash, tt.uuid, got, tt.want)
+			}
+		})
+	}
+
+	// 验证不同 uuid 产生不同 sessionKey
+	t.Run("different uuid different key", func(t *testing.T) {
+		hash := "sameprefix123456"
+		result1 := GenerateAnthropicDigestSessionKey(hash, "uuid0001-session-a")
+		result2 := GenerateAnthropicDigestSessionKey(hash, "uuid0002-session-b")
+		if result1 == result2 {
+			t.Errorf("Different UUIDs should produce different session keys: %s vs %s", result1, result2)
+		}
+	})
+}
+
+func TestAnthropicSessionTTL(t *testing.T) {
+	ttl := AnthropicSessionTTL()
+	if ttl.Seconds() != 300 {
+		t.Errorf("expected 300 seconds, got: %v", ttl.Seconds())
+	}
+}
+
+func TestBuildAnthropicDigestChain_ContentBlocks(t *testing.T) {
+	// 测试 content 为 content blocks 数组的情况
+	parsed := &ParsedRequest{
+		Messages: []any{
+			map[string]any{
+				"role": "user",
+				"content": []any{
+					map[string]any{"type": "text", "text": "describe this image"},
+					map[string]any{"type": "image", "source": map[string]any{"type": "base64"}},
+				},
+			},
+		},
+	}
+	result := BuildAnthropicDigestChain(parsed)
+	parts := splitChain(result)
+	if len(parts) != 1 {
+		t.Fatalf("expected 1 part, got %d: %s", len(parts), result)
+	}
+	if !strings.HasPrefix(parts[0], "u:") {
+		t.Errorf("expected prefix 'u:', got: %s", parts[0])
+	}
+}

backend/internal/service/gateway_multiplatform_test.go

@@ -232,6 +232,14 @@ func (m *mockGatewayCacheForPlatform) SaveGeminiSession(ctx context.Context, gro
 	return nil
 }
 
+func (m *mockGatewayCacheForPlatform) FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
+	return "", 0, false
+}
+
+func (m *mockGatewayCacheForPlatform) SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error {
+	return nil
+}
+
 type mockGroupRepoForGateway struct {
 	groups           map[int64]*Group
 	getByIDCalls     int

backend/internal/service/gateway_service.go

@@ -313,6 +313,14 @@ type GatewayCache interface {
 	// SaveGeminiSession 保存 Gemini 会话
 	// Save Gemini session binding
 	SaveGeminiSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error
+
+	// FindAnthropicSession 查找 Anthropic 会话（Trie 匹配）
+	// Find Anthropic session using Trie matching
+	FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool)
+
+	// SaveAnthropicSession 保存 Anthropic 会话
+	// Save Anthropic session binding
+	SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error
 }
 
 // derefGroupID safely dereferences *int64 to int64, returning 0 if nil
@@ -482,23 +490,25 @@ func (s *GatewayService) GenerateSessionHash(parsed *ParsedRequest) string {
 		return s.hashContent(cacheableContent)
 	}
 
-	// 3. Fallback: 使用 system 内容
+	// 3. 最后 fallback: 使用 system + 所有消息的完整摘要串
+	var combined strings.Builder
 	if parsed.System != nil {
 		systemText := s.extractTextFromSystem(parsed.System)
 		if systemText != "" {
-			return s.hashContent(systemText)
+			combined.WriteString(systemText)
 		}
 	}
-
-	// 4. 最后 fallback: 使用第一条消息
-	if len(parsed.Messages) > 0 {
-		if firstMsg, ok := parsed.Messages[0].(map[string]any); ok {
-			msgText := s.extractTextFromContent(firstMsg["content"])
+	for _, msg := range parsed.Messages {
+		if m, ok := msg.(map[string]any); ok {
+			msgText := s.extractTextFromContent(m["content"])
 			if msgText != "" {
-				return s.hashContent(msgText)
+				combined.WriteString(msgText)
 			}
 		}
 	}
+	if combined.Len() > 0 {
+		return s.hashContent(combined.String())
+	}
 
 	return ""
 }
@@ -541,6 +551,22 @@ func (s *GatewayService) SaveGeminiSession(ctx context.Context, groupID int64, p
 	return s.cache.SaveGeminiSession(ctx, groupID, prefixHash, digestChain, uuid, accountID)
 }
 
+// FindAnthropicSession 查找 Anthropic 会话（基于内容摘要链的 Fallback 匹配）
+func (s *GatewayService) FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
+	if digestChain == "" || s.cache == nil {
+		return "", 0, false
+	}
+	return s.cache.FindAnthropicSession(ctx, groupID, prefixHash, digestChain)
+}
+
+// SaveAnthropicSession 保存 Anthropic 会话
+func (s *GatewayService) SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error {
+	if digestChain == "" || s.cache == nil {
+		return nil
+	}
+	return s.cache.SaveAnthropicSession(ctx, groupID, prefixHash, digestChain, uuid, accountID)
+}
+
 func (s *GatewayService) extractCacheableContent(parsed *ParsedRequest) string {
 	if parsed == nil {
 		return ""
@@ -1104,7 +1130,6 @@ func (s *GatewayService) SelectAccountWithLoadAwareness(ctx context.Context, gro
 									result.ReleaseFunc() // 释放槽位
 									// 继续到负载感知选择
 								} else {
-									_ = s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL)
 									if s.debugModelRoutingEnabled() {
 										log.Printf("[ModelRoutingDebug] routed sticky hit: group_id=%v model=%s session=%s account=%d", derefGroupID(groupID), requestedModel, shortSessionHash(sessionHash), stickyAccountID)
 									}
@@ -1258,7 +1283,6 @@ func (s *GatewayService) SelectAccountWithLoadAwareness(ctx context.Context, gro
 						if !s.checkAndRegisterSession(ctx, account, sessionHash) {
 							result.ReleaseFunc() // 释放槽位，继续到 Layer 2
 						} else {
-							_ = s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL)
 							return &AccountSelectionResult{
 								Account:     account,
 								Acquired:    true,
@@ -2163,9 +2187,6 @@ func (s *GatewayService) selectAccountForModelWithPlatform(ctx context.Context,
 							_ = s.cache.DeleteSessionAccountID(ctx, derefGroupID(groupID), sessionHash)
 						}
 						if !clearSticky && s.isAccountInGroup(account, groupID) && account.Platform == platform && (requestedModel == "" || s.isModelSupportedByAccountWithContext(ctx, account, requestedModel)) && account.IsSchedulableForModelWithContext(ctx, requestedModel) {
-							if err := s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL); err != nil {
-								log.Printf("refresh session ttl failed: session=%s err=%v", sessionHash, err)
-							}
 							if s.debugModelRoutingEnabled() {
 								log.Printf("[ModelRoutingDebug] legacy routed sticky hit: group_id=%v model=%s session=%s account=%d", derefGroupID(groupID), requestedModel, shortSessionHash(sessionHash), accountID)
 							}
@@ -2266,9 +2287,6 @@ func (s *GatewayService) selectAccountForModelWithPlatform(ctx context.Context,
 						_ = s.cache.DeleteSessionAccountID(ctx, derefGroupID(groupID), sessionHash)
 					}
 					if !clearSticky && s.isAccountInGroup(account, groupID) && account.Platform == platform && (requestedModel == "" || s.isModelSupportedByAccountWithContext(ctx, account, requestedModel)) && account.IsSchedulableForModelWithContext(ctx, requestedModel) {
-						if err := s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL); err != nil {
-							log.Printf("refresh session ttl failed: session=%s err=%v", sessionHash, err)
-						}
 						return account, nil
 					}
 				}
@@ -2377,9 +2395,6 @@ func (s *GatewayService) selectAccountWithMixedScheduling(ctx context.Context, g
 						}
 						if !clearSticky && s.isAccountInGroup(account, groupID) && (requestedModel == "" || s.isModelSupportedByAccountWithContext(ctx, account, requestedModel)) && account.IsSchedulableForModelWithContext(ctx, requestedModel) {
 							if account.Platform == nativePlatform || (account.Platform == PlatformAntigravity && account.IsMixedSchedulingEnabled()) {
-								if err := s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL); err != nil {
-									log.Printf("refresh session ttl failed: session=%s err=%v", sessionHash, err)
-								}
 								if s.debugModelRoutingEnabled() {
 									log.Printf("[ModelRoutingDebug] legacy mixed routed sticky hit: group_id=%v model=%s session=%s account=%d", derefGroupID(groupID), requestedModel, shortSessionHash(sessionHash), accountID)
 								}
@@ -2482,9 +2497,6 @@ func (s *GatewayService) selectAccountWithMixedScheduling(ctx context.Context, g
 					}
 					if !clearSticky && s.isAccountInGroup(account, groupID) && (requestedModel == "" || s.isModelSupportedByAccountWithContext(ctx, account, requestedModel)) && account.IsSchedulableForModelWithContext(ctx, requestedModel) {
 						if account.Platform == nativePlatform || (account.Platform == PlatformAntigravity && account.IsMixedSchedulingEnabled()) {
-							if err := s.cache.RefreshSessionTTL(ctx, derefGroupID(groupID), sessionHash, stickySessionTTL); err != nil {
-								log.Printf("refresh session ttl failed: session=%s err=%v", sessionHash, err)
-							}
 							return account, nil
 						}
 					}

backend/internal/service/gemini_multiplatform_test.go

@@ -281,6 +281,14 @@ func (m *mockGatewayCacheForGemini) SaveGeminiSession(ctx context.Context, group
 	return nil
 }
 
+func (m *mockGatewayCacheForGemini) FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
+	return "", 0, false
+}
+
+func (m *mockGatewayCacheForGemini) SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error {
+	return nil
+}
+
 // TestGeminiMessagesCompatService_SelectAccountForModelWithExclusions_GeminiPlatform 测试 Gemini 单平台选择
 func TestGeminiMessagesCompatService_SelectAccountForModelWithExclusions_GeminiPlatform(t *testing.T) {
 	ctx := context.Background()

backend/internal/service/openai_gateway_service_test.go

@@ -220,6 +220,14 @@ func (c *stubGatewayCache) SaveGeminiSession(ctx context.Context, groupID int64,
 	return nil
 }
 
+func (c *stubGatewayCache) FindAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain string) (uuid string, accountID int64, found bool) {
+	return "", 0, false
+}
+
+func (c *stubGatewayCache) SaveAnthropicSession(ctx context.Context, groupID int64, prefixHash, digestChain, uuid string, accountID int64) error {
+	return nil
+}
+
 func TestOpenAISelectAccountWithLoadAwareness_FiltersUnschedulable(t *testing.T) {
 	now := time.Now()
 	resetAt := now.Add(10 * time.Minute)